Imaging lens

ABSTRACT

Disclosed herein is an imaging lens suitable for a camera module using a high resolution imaging sensor, decreasing a flare phenomenon and reducing the sensitivity. The imaging lens comprises, in order from the object side, a first lens having positive (+) refractive force; a second lens having negative (−) refractive force; a third lens having positive (+) refractive force; a fourth lens having positive (+) refractive force; and a fifth lens having negative (−) refractive force, wherein an object side plane of the third lens is convexly formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/854,428, filed Aug. 11, 2010, which claims the benefit under 35U.S.C. §119 of Korean Patent Application No. 10-2009-0073715, filed onAug. 11, 2009, which are hereby incorporated by reference in theirentirety.

BACKGROUND

1. Field of the Invention

The present invention relates to an imaging lens.

2. Description of the Related Art

Regarding an image pick-up system, there have been recent researchesinto mobile terminal used camera modules, DSCs (Digital Still Camera),camcorders, PC cameras (imaging lens attached personal computers), etc.The most important component to obtain an image for such an imagepick-up system-related camera module is an imaging lens that producesimages.

Attempts to construct an imaging lens of high resolution using 5 piecesof lenses have been previously made. Each of the five pieces of lensesis comprised of lenses with positive (+) refractive force and lenseswith negative (−) refractive force. For example, the imaging lens isconstructed with PNNPN (+−−+−), PNPNN (+−+−−) or PPNPN (++−+−) orderlyfrom an object side. However, an image module of the above-mentionedstructure, in some cases, fails to show satisfactory optical propertiesor aberration properties, and thus a high resolution imaging lens havinga new power structure is required.

BRIEF SUMMARY

The present invention provides an imaging lens having a new powerstructure, in particular provides an imaging lens configured to reduce aflare phenomenon, characteristically decrease the sensitivity and have asuperior aberration property.

An imaging lens according to an embodiment of the present inventionincludes, in order from an object side, a first lens having positive (+)refractive force; a second lens having negative (−) refractive force; athird lens having positive (+) refractive force; a fourth lens havingpositive (+) refractive force; and a fifth lens having a negative (−)refractive force, wherein the third lens is convexly formed at thesurface of the object side.

In an imaging lens according to the present embodiment, a certain lensis formed in which the first lens, the third lens and the fourth lenshave positive (+) power, and the second lens and the fifth lens havenegative (−) power, that is, providing an imaging lens of PNPPN powerstructure.

Also, the third lens is convexly formed at the surface of an object sidepossibly to realize an imaging lens where the aberration property issuperior, a flare phenomenon decreases and the sensitivity is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a construction view of an imaging lens according to thepresent embodiment;

FIG. 2 is a graph showing an aberration property according to oneembodiment of the present invention;

FIGS. 3A and 3B are graphs showing a coma-aberration according to oneembodiment of the present invention;

FIG. 4 is a graph showing a sensitivity decrease property according tothe present embodiment; and

FIGS. 5 a and 5 b are graphs showing a flare phenomenon decreasingproperty according to the present embodiment.

DETAILED DESCRIPTION

Since various changes can be made to the present invention and variouskinds of embodiments can be implemented, specific embodiments will beillustrated in the drawings and intended to be described in the detaileddescription in detail. However, it should not be appreciated in alimiting sense of limiting the present invention to a specific practicebut to include all the changes, equivalents and replacements which fallin the spirit and technological scope of the present invention.

Stated that any component “is connected” or “is conjunctive” to anothercomponent, it will be appreciated to be directly connected orconjunctive to the very another component or that there exists the othercomponent in the middle.

In the following, referring to attached drawings a preferred embodimentaccording to the present invention will be described in detail, butwithout regard to a drawing sign an identical or corresponding componentis assigned the same reference numeral and a redundant description ofthis will be omitted.

FIG. 1 is a construction view according to the present embodiment, andis particularly a lateral construction diagram exemplifying thedisposition state of a lens in an optic axis (ZO) center. In theconstruction view of FIG. 1, the thickness, size and shape of a lenshave been somewhat exaggerated for description, and a spherical oraspheric shape is only presented as one embodiment not limiting to suchshapes.

Referring to FIG. 1, a camera lens module of the present invention has aconstruction disposed of a first lens 10, a second lens 20, a third lens30, a fourth lens 40, a fifth lens 50, a filter 60 and a light-receivingdevice 70 orderly from the object side.

Light corresponding to image information of a subject passes through thefirst lens 10, the second lens 20, the third lens 30, the fourth lens40, the fifth lens 50 and the filter 60 and is incident on thelight-receiving device 70.

Hereinafter in the description of the construction of each lens, “Objectside surface” means the surface of a lens facing an object side withrespect to an optical axis, and “Image side surface” means the surfaceof the lens facing an imaging surface with respect to the optical axis.

The first lens 10 has positive (+) refractive force, and there is theobject side surface S1 convexly formed. The object side surface S1 ofthe first lens 10 may act as an aperture, and in this case, an imaginglens of the present embodiment does not need a separate aperture. Thesecond lens has negative (−) refractive force, and there is the objectside surface S3 convexly formed.

In the third lens 30, the fourth lens 40 and the fifth lens 50, theobject side surface and the image side surface are all comprised of anaspheric. (That is, each of object side planes and image side planes inthe third lens, the fourth lens and the fifth lens is of asphericplane.) And, the third lens 30 and the fourth lens 40 have positive (+)refractive force, and the fifth lens has negative (−) refractive force.

As shown in the figure, the third lens 30 is a meniscus form where theobject side surface S5 is convexly formed. And, the refractive force ofthe third lens 30 is formed smaller than the refractive force of theremaining lenses. The object side surface S5 of the third lens 30 isconvexly formed, so that as a result a flare phenomenon spreading imagesdecreases and the sensitivity of a lens is reduced.

The fourth lens 40 is a meniscus form in which the object side surfaceS7 is concavely formed, and the fifth lens 50 is a meniscus form wherethe object side surface S9 is convexly formed.

Here, the fifth lens 50 is an aspheric shape in which the double-sidesof the object side surface S9 and the image side surface S10 all have aninflection point. As shown in the figure, the image side surface S10 ofthe fifth lens 50 bends towards the image side as proceeding from acentral part centering an optical axis ZO to the peripheral and againbends to the object side as proceeding from the peripheral part awayfrom the optical axis ZO to the outermost angle region, so as to form anaspheric inflection point.

An aspheric inflection point formed in the fifth lens 50 may adjust themaximum emergence angle of key light incident on a light-receivingdevice 70. And, an aspheric inflection point formed in the object sidesurface S9 and the image side surface S10 of the fifth lens 40 adjuststhe maximum emergence angle of key light, thereby preventing the shadingof the screen's surrounding part.

The filter 60 is at least one filter of optical filters such as aninfrared filter and a cover glass. As a filter 60, in the application ofthe infrared filter, it blocks radiant heat emitting from external lightfrom being transferred to the light-receiving device 70. Also, theinfrared filter transmits visible light and reflects infrared rays tooutput it to the outside.

The light-receiving device 70 is an image sensor, for example, CCD(Charge Coupled Device) or CMOS (Complementary Metal OxideSemiconductor), etc.

The first lens 10, the second lens 20, the third lens 30, the fourthlens 40 and the fifth lens 50 uses an aspheric lens as later describedin embodiments, possibly improving the resolution of a lens and having agood point of superior aberration property.

Because the later described conditional expressions and embodiments arepreferred embodiments raising the effect of interaction, it would beobvious to those skilled in the art that the present invention is notnecessarily comprised of the following conditions. For example, only bygratifying some conditions of later described conditional expressions,the lens construction of the present invention may have a raised effectof interaction.

[Condition 1] 3<L1R1<7

[Condition 2] L3R1>1

[Condition 3] L3R2>1

[Condition 4] 0.5<f1/f<1.5

[Condition 5] 0.5<T/f<1.5

[Condition 6] 1.6<N2<1.7

[Condition 7] 1.5<N1, N3, N4, N5<1.6

[Condition 8] 20<V2<30

[Condition 9] 50<V1, V3, V4, V5<60

Herein, L1R1: the object side surface radius of the first lens

L3R1: the object side surface radius of the third lens

L3R2: the imaging side surface of the third lens

f: the entire focus distance of the imaging lens

f1: the focus distance of the first lens

T: the distance from the object side surface to the on-focus surface ofthe first lens

N1˜N5: the refractive index of the first lens˜the fifth lens

V1˜V5: Abbe's number of the first lens˜the fifth lens

Condition 1 specifies the curvature radius at the object side surface S1of the first lens 10, Conditions 2 and 3 specify the double-sidecurvature radius of the third lens 30. The specification of thecurvature radius is conditions on a lens's shape, and this is for thecompensation of coma aberration and astigmatism and reducing themanufacturing tolerance.

Condition 4 specifies the refractive force of the first lens 10. Thefirst lens 10 has refractive force with appropriate chromatic aberrationand the pertinent compensation of spherical aberration by Condition 4.Condition 5 specifies the dimension of the optical axis direction of theentire optical system, and it is a condition for ultra-small lens and acondition for appropriate aberration compensation.

Conditions 6 and 7 specify refractive index of each lens, and Conditions8 and 9 specify Abbe's number of each lens. The specification ofrefractive index and Abbe's number of each lens is a condition forbetter compensation of chromatic aberration.

Hereinafter, the action and effect of the present invention will bedescribed with reference to a specific embodiment. Aspheric mentioned ina later embodiment is obtained from a known Equation 1, and ‘E and itssucceeding number’ used in Conic constant k and aspheric coefficient A,B, C, D, E, F indicates 10's power. For example, E+01 denotes 10¹, andE-02 denotes 10⁻².

$\begin{matrix}{z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{4} + {CY}^{4} + {DY}^{4} + {EY}^{4} + {FY}^{4} + \ldots}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Herein, z: Distance from the lens's top-point to an optical axisdirection

c: Basic curvature of a lens

Y: Distance towards a direction perpendicular to an optical axis

K: Conic constant

A, B, C, D, E, F: Aspheric coefficient

WORKING EXAMPLE

TABLE 1 Work example f 4.75 f1 4.04 f2 −4.55 f3 9.58 f4 3.13 f5 −3.23f1/f 0.85 T 6.73 T/f 1.42 N1 1.533 V1 56.5 N2 1.62 V2 26 N3, N4, N51.533 V3, V4, V5 56.5 L1R1 5.60 L3R1 3.20 L3R2 8.00

Table 1 shows a work example matching the aforementioned conditionalexpressions.

Referring to Table 1, L1R1 is 5.60 that matches to Condition 1, and L3R1is 3.20 and L3R2 is 8.00, respectively matching into Conditions 2 and 3.Also, f1/f is 0.85 that matches into Condition 4, and T/f is 1.42showing a matching into Condition 5. Also, it can be seen that therefractive index N1˜N5 of each lens matches Conditions 6 and 7, andAbbe's number V1˜V5 of each lens matches Conditions 8 and 9.

TABLE 2 Surface Curvature Thickness or Refractive Number Radius (R)Distance (d) Index (N) 1* 5.6 0.9 1.53 2* −3.5 0.27 3* 9.4 0.40 1.61 4*2.1 0.30 5* 3.2 0.55 1.53 6* 8.0 0.62 7* −2.8 1.0 1.53 8* −1.2 0.1 9*3.4 0.78 1.53 10*  1.1 0.70 11  0.3 1.52 12  0.80 image 0.01

In the above Table 2, the notation * which is further written near thesurface number indicates aspheric.

The embodiment of Table 2 shows a more specific embodiment than Table1's embodiment.

And, the aspheric coefficient values of each lens in the embodiment ofTable 2 are as in the following table 3.

TABLE 3 Surface Number k A B C D E F 1* 0 −0.278840E−01 −0.115063E−01 −0.314565E−02 0.436500E−02 −0.364702E−02 0 2* 0 −0.691104E−02−0.212701E−01   0.124050E−01 −0.861190E−02   0.297906E−02 0 3* 0−0.193793E−01 0.103822E−01 −0.133796E−02 −0.148393E−02   0.104056E−02 04* −4.310108 −0.198769E−01 0.309275E−01 −0.153250E−01 0.316803E−02−0.164905E−04 0 5* 0 −0.508923E−01 0.134434E−01 −0.118161E−02 0 0 0 6* 0−0.184251E−01 0.197696E−02  0.142627E−03 0 0 0 7* −8.536520−0.287370E−01 0.202006E−01 −0.841387E−02 0.244085E−02 −0.357293E−03 0 8*−1.771588  0.303330E−01 −0.176527E−01   0.367535E−02 0.161459E−03−0.760293E−04 0 9* −53.45174 −0.127200E−02 −0.878231E−02   0.148096E−02−0.792305E−05  −0.165005E−04 0.915831E−06 10*  −5.030395 −0.213867E−010.309764E−02 −0.604438E−03 0.690919E−04 −0.372236E−05 0.467587E−07

FIG. 2 is a graph showing an aberration view according to theaforementioned embodiment, in particular a graph measuring alongitudinal spherical aberration, astigmatic field curves and adistortion in order from the left.

In FIG. 2, the Y axis means the image size, and the X axis means thefocus distance (mm unit) and the distortion rate (% unit). In FIG. 2, asthe curves approach the Y axis, an aberration compensation function isinterpreted to be good. In the shown aberration view, images' values onalmost all the fields appear adjacent to the Y axis, so that thelongitudinal spherical aberration, the astigmatic field curves and thedistortion all show superior numerical values.

FIG. 3 is a graph measuring Coma aberration, and FIGS. 3( a) and 3(b) isa graph measuring tangential aberration and sagittal aberration of eachwavelength according to a field height. In FIG. 3, In FIG. 3, as a graphshowing a test result approaches the X axis from the positive axis andthe negative axis each, a coma aberration compensation function isinterpreted to be good. In the FIG. 3's measurement examples, imagevalues on almost all the fields appear adjacent to the X axis, so thatall of them are analyzed to show a superior coma aberration compensationfunction.

FIG. 4 is a graph showing a sensitivity decrease feature as a result ofthe present embodiment, and FIGS. 5 a-5 b show a flare phenomenonreduction feature according to the present embodiment. In FIG. 4 andFIGS. 5 a-5 b, to show the sensitivity decrease and the reduction of aflare phenomenon by bulgingly forming the object side surface S5 of thethird lens 30 in the present invention, a case of concavely forming theobject side surface S5 of the third lens 30 and a case of convexlyforming the same are exemplified in comparison to each other.

FIG. 4 a shows a tolerance analysis in a lens plane when the object sideS5 of the third lens 30 is concave, and FIG. 4 b shows a toleranceanalysis in the lens plane when the object side S5 of the third lens 30is convex. Comparing the two views, it can be known that the change inresolution (MTF; Modulation Transfer Function) at FIG. 4 b is smallerthan FIG. 4 a. That is, when the third lens 30 has a meniscus form inwhich the object side surface S5 is convex, it clearly causes thefurther decrease of its sensitivity than in a concave form of the objectside surface of the third lens 30.

FIG. 5 a shows an example of ray distribution in an image sensor wherethe object side surface S5 of the third lens 30 is concave, and FIG. 5 bshows an example of ray distribution in the image sensor when the objectside surface S5 of the third lens 30 is convex. Comparing the two views,the ray distribution at FIG. 5 b is well dispersed than in FIG. 5 a, andthus, to be sure, a ghost phenomenon or a flare phenomenon, in which animage non-existent in a subject is formed when the object side surfaceof the third lens 30 is in a convex shape like the present invention, isgreatly decreased.

While the embodiments of the present invention has been explained indetail at the foregoing part, the rights scope of the present inventionis not limited to the embodiment and various modifications andsubstitutions thereto by those skilled in the art using the basicconcept of the present invention as defined in the accompanying claimswill fall in the rights scope of the invention.

What is claimed is:
 1. An imaging lens system, comprising five lenses,in an order from an object side to an image side: a first lens havingpositive (+) refractive power; a second lens having negative (−)refractive power; a third lens having positive (+) refractive powerwhich is different from the refractive power of the second lens; afourth lens having positive (+) refractive power; and a fifth lenshaving refractive power, wherein an object-side surface of the fourthlens is concavely formed at an optical axis, and both surfaces of thefifth lens are aspheric; wherein the refractive power of the third lensis smaller than that of the first, second, fourth, or fifth lens.
 2. Theimaging lens system as claimed in claim 1, wherein each of theobject-side surfaces and the image-side surfaces of the third lens andthe fourth lens is aspheric.
 3. The imaging lens system as claimed inclaim 1, wherein an object-side surface of the third lens is convexlyformed at the optical axis.
 4. The imaging lens system as claimed inclaim 1, wherein an image-side surface of the fifth lens is concavelyformed at the optical axis.
 5. The imaging lens system as claimed inclaim 1, wherein the fifth lens has at least one inflection point. 6.The imaging lens system as claimed in claim 1, wherein the imaging lenssystem has a stop on an object-side surface of the first lens.
 7. Theimaging lens system as claimed in claim 1, wherein an image-side surfaceof the fourth lens is convexly formed at the optical axis.
 8. Theimaging lens system as claimed in claim 1, wherein the imaging lenssystem meets a conditional expression of 0.5<f1/f<1.5, where an entirefocus distance of the imaging lens system is f and a focus distance ofthe first lens is f1.
 9. The imaging lens system as claimed in claim 1,wherein the imaging lens system meets a conditional expression of0.5<T/f<1.5, where an entire focus distance of the imaging lens systemis f and a distance from the object-side surface of the first lens to anon-focus surface is T.
 10. The imaging lens system as claimed in claim1, wherein the imaging lens system meets a conditional expression of1.6<N2<1.7, where N2 is a refractive index of the second lens.
 11. Theimaging lens system as claimed in claim 1, wherein the imaging lenssystem meets a conditional expression of 20<V2<30, where V2 is an Abbe'snumber of the second lens.
 12. The imaging lens system as claimed inclaim 1, wherein the third lens, the fourth lens, and the fifth lenseach is a lens in a meniscus form.
 13. An imaging lens system,comprising five lenses, in an order from an object side to an imageside: a first lens having positive (+) refractive power; a second lenshaving negative (−) refractive power; a third lens having positive (+)refractive power which is different from the refractive power of thesecond lens; a fourth lens having positive (+) refractive power; and afilth lens having a refractive power, wherein an object-side surface ofthe fourth lens is concavely formed at an optical axis, and bothsurfaces of the third lens are aspheric; wherein the refractive power ofthe third lens is smaller than that of the first, second, fourth, orfifth lens.
 14. The imaging lens system as claimed in claim 13, whereinthe imaging lens system meets a conditional expression of 0.5<f1/f<1.5,where an entire focus distance of the imaging lens system is f and afocus distance of the first lens is f1.
 15. The imaging lens system asclaimed in claim 13, wherein the imaging lens system meets a conditionalexpression of 0.5<T/f<1.5, where an entire focus distance of the imaginglens system is f and a distance from an object-side surface of the firstlens to an on-focus surface is T.
 16. The imaging lens system as claimedin claim 13, wherein the fifth lens has at least one inflection point.17. A camera module comprising an imaging lens system and an imagesensor: wherein the imaging lens system comprising five lenses, in anorder from an object side to an image side: a first lens having positive(+) refractive power: a second lens having negative (−) refractivepower; a third lens having positive (+) refractive power which isdifferent from the refractive power of the second lens; a fourth lenshaving positive (+) refractive power; and a fifth lens having refractivepower, wherein an object-side surface of the fourth lens is concavelyformed at an optical axis, and both surfaces of the fifth lens areaspheric; wherein the refractive power of the third lens is smaller thanthat of the first, second, fourth, or fifth lens.